Image stitching, as an important subject in the image processing field, has a promising application prospect. For instance, during medical image processing, due to limitation in the size of a medical imaging apparatus, it is sometimes hard to image an object completely at one time. For instance, when using a nuclear magnetic resonance imaging apparatus to scan the spine of a patient, only part of the spine of the patient can be imaged at each scanning. In this case, the images obtained from multiple times of scanning should be stitched to obtain an image of the whole spine.